I'd like to offer my observation and long comment regarding "loose" wheel nuts. I read all the time in the discussion forums (for all colors of tractors) regarding tractor wheel nuts loosening. I noticed this on my own tractor as well. I was curious about the cause as you almost never hear about car or truck wheel nuts coming loose. Oh sure, occassionally, I see a car driving around with missing nuts or studs but that is the exception rather than the rule.
Last week, I had the occassion to switch my tires around to change from narrow to wide position. Based on my observations, I believe the cause is several fold:
(1) The tractors use Bolts as opposed to studs, which is used on most automobiles. The argument regarding the use of studs vs bolts can be researched through an internet search but many experts believe that studs provide more accurate and consistent torque loading because when you torque bolts to secure a load, the fastener is actually being "twisted" while it's being torqued to the proper reading. Accordingly, the bolt is reacting to two different forces simultaneously. A stud, of course does not have this problem.
(2) It seems to me that the fit of the bolts is rather loose and there is more freeplay than I would like to see. If the tolerances can be tightened up, I think the propensity for the bolts to loosen will diminish significantly.
(3) This is a big one: Automobile wheels usually get sandwiched tightly between the nut and the hub, and once torqued, there is no freeplay when the vehicle is operated since there is no gap between the hub-wheel-nut. You'll notice on car rims, once tightened, any further torquing of the nuts will only serve to "stretch" the bolts and not take up any more air gap.
On MY tractor, at least, I see there are raised areas spaced around the center of the wheel between the bolt holes and these are the areas that contact the hub; the immediate areas of the bolt holes do not actually contact the hub but float slightly above. It seems to me that when tightened, the bolts will actually causes the metal on the rim to flex towards the hub. In my opinion, this is a poor design. Firstly, torquing one bolt will cause the rim (or hub backing plate) to flex slightly thereby causing an adjacent bolt to loose some torque. It is important to torque them all more than once around. Secondly, the M16 bolts installed on my tractor only calls for 103 ft/lbs of torque. This is almost surely to prevent the rim from getting bent out of shape from the torquing process since these bolts can surely take a lot more torque. Because there is an air gap at the bolt hole location, these bolts can be tightened significant further to close up that gap. Doing so, however, will almost surely damage the rim beyond serviceability. The recommended "normal" torque rating for an 8.8 grade M16 bolt, according to my Snapon torque wrench is 188 ft/lbs. Therefore, the 103 ft/lb specified torque is way below where the bolts should be to provide the clamping force that is common on fasteners of this size. Unfortunately, it is not possible to torque them that high as again, there is no metal to metal contact between rim (at bolt location) and hub backing plate. That brings us to (3), which is that when the rim is torqued to specifications, the air gap allows the rim room to flex during usage. Oh, I know that 103 ft lbs is a lot and the metal is fairly thick but the tractor is quite hefty and those are huge rims. Factor in the dynamic forces and huge torque numbers at the rims and side loads, etc and momentary flexing is not impossible. Imagine, if you will, a short and heavy springboard that is being held down at the springy end by a bolt. If that bolt is tightened so that there is no gap between the board and the surface it is fastened to, then it is very difficult to get that bolt to loosen. If, instead, the bolt is tightened but some space is left so that there is a gap between the board and the surface it is being clamped to, bouncing on the board will almost surely cause the bolt to loosen over time. So it is as well with the wheel. The daily flexing of the rim during usage will in my opinion always cause the bolts to loosen unless there is always some friction (threadlock?) on the bolt threads or head to prevent rotation. Placing small appropriate spacers behind the bolt holes so that the bolt heads and rim and hub all contact each other when clamped will permit the fasteners to be tightened to it's full potential provided the hub backing material will accommodate that amount of torque. This will almost surely resolve the loosen nut problem. However, since this is not the factory recommended method, I offer this only as my observation and not a recommendation.
I understand that this does nothing to help the original poster regarding wheel nut sizing, but this is food for thought regarding why the darn things keep coming loose!
